From: Oliver Upton <oliver.upton@linux.dev>
To: Marc Zyngier <maz@kernel.org>
Cc: James Morse <james.morse@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
kvmarm@lists.linux.dev, Zenghui Yu <yuzenghui@huawei.com>,
linux-arm-kernel@lists.infradead.org,
Sean Christopherson <seanjc@google.com>
Subject: Re: [PATCH v2 4/4] KVM: arm64: Use config_lock to protect vgic state
Date: Thu, 23 Mar 2023 19:18:05 +0000 [thread overview]
Message-ID: <ZByl7ZB835jySq/x@linux.dev> (raw)
In-Reply-To: <87o7olgfjs.wl-maz@kernel.org>
On Wed, Mar 22, 2023 at 12:02:15PM +0000, Marc Zyngier wrote:
> On Thu, 16 Mar 2023 21:14:12 +0000,
> Oliver Upton <oliver.upton@linux.dev> wrote:
[...]
> > --- a/arch/arm64/kvm/vgic/vgic-its.c
> > +++ b/arch/arm64/kvm/vgic/vgic-its.c
> > @@ -2043,7 +2043,10 @@ static int vgic_its_attr_regs_access(struct kvm_device *dev,
> > if (offset & align)
> > return -EINVAL;
> >
> > - mutex_lock(&dev->kvm->lock);
> > + if (!lock_all_vcpus(dev->kvm))
> > + return -EBUSY;
> > +
> > + mutex_lock(&dev->kvm->arch.config_lock);
>
> Huh, that's fishy. The whole "lock the VM and the lock the individual
> vcpus" is there to prevent a concurrent creation of a vcpu while we're
> doing stuff that affects them all. Allowing a new vcpu to come online
> while this sequence is happening is ... unexpected.
>
> Why do we need to drop this initial lock? I'd expect them to be
> completely cumulative.
Urgh.. Yes, you're right. I'll go with kvm->lock -> lock_all_vcpus() ->
kvm->config_lock in the next spin to guard against the vCPU creation
race.
--
Thanks,
Oliver
next prev parent reply other threads:[~2023-03-23 19:18 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-16 21:14 [PATCH v2 0/4] KVM: arm64: Fix vcpu->mutex v. kvm->lock inversion Oliver Upton
2023-03-16 21:14 ` [PATCH v2 1/4] KVM: arm64: Avoid vcpu->mutex v. kvm->lock inversion in CPU_ON Oliver Upton
2023-03-22 12:02 ` Marc Zyngier
2023-03-23 19:47 ` Oliver Upton
2023-03-16 21:14 ` [PATCH v2 2/4] KVM: arm64: Avoid lock inversion when setting the VM register width Oliver Upton
2023-03-22 12:02 ` Marc Zyngier
2023-03-23 19:20 ` Oliver Upton
2023-03-23 19:43 ` Marc Zyngier
2023-03-23 19:49 ` Oliver Upton
2023-03-23 20:09 ` Jeremy Linton
2023-03-23 20:45 ` Oliver Upton
2023-03-23 22:45 ` Jeremy Linton
2023-03-16 21:14 ` [PATCH v2 3/4] KVM: arm64: Use config_lock to protect data ordered against KVM_RUN Oliver Upton
2023-03-16 21:14 ` [PATCH v2 4/4] KVM: arm64: Use config_lock to protect vgic state Oliver Upton
2023-03-22 12:02 ` Marc Zyngier
2023-03-23 19:18 ` Oliver Upton [this message]
2023-03-23 22:48 ` [PATCH v2 0/4] KVM: arm64: Fix vcpu->mutex v. kvm->lock inversion Jeremy Linton
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=ZByl7ZB835jySq/x@linux.dev \
--to=oliver.upton@linux.dev \
--cc=james.morse@arm.com \
--cc=kvmarm@lists.linux.dev \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=maz@kernel.org \
--cc=seanjc@google.com \
--cc=suzuki.poulose@arm.com \
--cc=yuzenghui@huawei.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).